1 Find a piece of string or strip of paper no wider than 3/4". 2 Wrap it around the base of the appropriate finger. 3 Use a pen to mark the point on the string/paper where it overlaps, forming a complete circle. 4 With a ruler, measure the length from the starting end of the string/paper to the pen mark. 5 Use this measurement and the chart to the right to determine your ring size.